Espresso/drivers/fs/sfs.c

#include <drivers/ide.h>
#include <stdio.h>
#include <stdlib.h>

#include <fs/sfs.h>


#define SFS_HEADER_START_LBA 8
#define SFS_HEADER_REGION_SECTORS 1024
#define SFS_HEADERS_PER_SECTOR 8
#define TOTAL_SECTORS 32768
#define SFS_DATA_START_LBA (TOTAL_SECTORS / 4)


#pragma pack(push, 1)
typedef struct sfs_file_header {
  uint16_t magic; /* 0xBEEF */
  /*
    32 chars for the filename itself,
    4 chars for the file's extension,
    and 1 char for the null zero.
  */
  char filename[37];
  
  uint64_t data_beginning; /* Actually a 48 bit LBA mind you */
  uint32_t num_sectors; /* Number of sectors after data_beginning that are this file's data */
  
  uint8_t padding[13]; /* Padding to 64 bytes total */
} sfs_file_header_t;
#pragma pack(pop)


uint8_t buffer[512] = { 0 };

/* Global allocator pointer to the next free sector in the data region */
uint64_t sfs_next_free_data_sector = SFS_DATA_START_LBA;



int32_t sfs_init(void)
{
  uint8_t sector_buf[512];

  for (uint64_t lba = SFS_HEADER_START_LBA; lba < SFS_HEADER_START_LBA + SFS_HEADER_REGION_SECTORS; ++lba)
  {
    if (read_sector(lba, sector_buf) != 0)
    {
      return -1;
    }

    sfs_file_header_t* hdr = (sfs_file_header_t*)sector_buf;

    if (hdr->magic == 0xBEEF)
    {
      uint64_t end = hdr->data_beginning + hdr->num_sectors;
      if (end > sfs_next_free_data_sector)
      {
        sfs_next_free_data_sector = end;
      }
    }

    /* TODO: support multiple headers per sector, loop through all 512/64 = 8 headers here */
  }

  return 0;
}

bool sfs_get_formatted_name(const char* raw_name, char output[37])
{
  size_t len = strlen(raw_name);

  if (len > 36 || strchr(raw_name, '/') || strchr(raw_name, '*') || strchr(raw_name, '\\')) {
    return false;
  }

  memset(output, ' ', 36);
  output[36] = '\0';

  memcpy(output, raw_name, len);

  return true;
}

int32_t sfs_create_file(const char* _name, int32_t size_bytes)
{
  if (size_bytes < 0)
  {
    return -1;
  }

  char name[37];
  if (!sfs_get_formatted_name(_name, name))
  {
    return -2;
  }

  uint32_t sectors_needed = (size_bytes + 511) / 512;
  uint8_t sector_buf[512];

  for (uint64_t lba = SFS_HEADER_START_LBA; lba < SFS_HEADER_START_LBA + SFS_HEADER_REGION_SECTORS; ++lba)
  {
    if (read_sector(lba, sector_buf) != 0)
    {
      return -3;
    }

    for (int i = 0; i < SFS_HEADERS_PER_SECTOR; ++i)
    {
      sfs_file_header_t* hdr = ((sfs_file_header_t*)sector_buf) + i;

      if (hdr->magic != 0xBEEF)
      {
        hdr->magic = 0xBEEF;
        memcpy(hdr->filename, name, 37);
        hdr->data_beginning = sfs_next_free_data_sector;
        hdr->num_sectors = sectors_needed;

        sfs_next_free_data_sector += sectors_needed;

        if (write_sector(lba, sector_buf) != 0)
        {
          return -4;
        }

        return 0;
      }
    }
  }

  return -5;
}


/*
  num is number of bytes
  Note: if a negative value is passed for num, then read the whole file
*/
int32_t sfs_read_file(char* _name, void* buffer, int32_t num)
{
  char name[37] = { '\0' };
  
  if (!sfs_get_formatted_name(_name, name))
  {
    return -1;
  }
  
  memclr(buffer, sizeof(buffer)); /* Zero out buffer */
  
  uint64_t j = SFS_HEADER_START_LBA;
  
  if (read_sector(j, buffer) != 0)
  {
    return -2;
  }
  
  sfs_file_header_t file;
  
  memcpy(&file, buffer, sizeof(file));
  
  if (file.magic != 0xBEEF)
  {
    return -3;
  }
  
  while (strncmp(file.filename, name, 37) != 0)
  {
    memclr(buffer, sizeof(buffer));
    
    if (read_sector(++j, buffer) != 0)
    {
      return -4;
    }
    
    memcpy(&file, buffer, sizeof(file));
    
    if (file.magic != 0xBEEF)
    {
      return -5;
    }
  }
  
  /* File found, now to read data */
  
  uint32_t sectors_to_read = file.num_sectors;
  if (num >= 0)
  {
    uint32_t max_sectors = (num + 511) / 512;
    
    if (max_sectors < sectors_to_read)
    {
      sectors_to_read = max_sectors;
    }
  }

  for (uint32_t i = 0; i < sectors_to_read; ++i)
  {
    if (read_sector((uint64_t)(file.data_beginning) + i, (uint8_t*)buffer + i * 512) != 0)
    {
      return -6; /* read error */
    }
  }

  return sectors_to_read * 512;
  
  memclr(buffer, sizeof(buffer));
  
  return 0;
}

/*
  Writes num bytes to an existing file.
  If the file exists, it will be resized (grown/shrunk) to fit num bytes.
  Returns number of bytes written (rounded up to sectors), or a negative error code.
*/
int32_t sfs_write_file(char* _name, const void* buffer, int32_t num)
{
  if (num < 0)
  {
    return -1;
  }

  char name[37] = { '\0' };
  if (!sfs_get_formatted_name(_name, name))
  {
    return -2;
  }

  uint8_t sector_buf[512];
  uint64_t header_lba = SFS_HEADER_START_LBA;
  sfs_file_header_t file;

  while (1) {
    if (read_sector(header_lba, sector_buf) != 0)
    {
      return -3;
    }

    memcpy(&file, sector_buf, sizeof(file));
    
    if (file.magic != 0xBEEF)
    {
      return -4;
    }

    if (strncmp(file.filename, name, 37) == 0)
    {
      break;
    }

    ++header_lba;
  }

  uint32_t sectors_needed = (num + 511) / 512;

  if (sectors_needed != file.num_sectors)
  {
    file.num_sectors = sectors_needed;
    file.data_beginning = sfs_next_free_data_sector;
    sfs_next_free_data_sector += sectors_needed;
  }

  file.magic = 0xBEEF;
  memcpy(sector_buf, &file, sizeof(file));
  
  if (write_sector(header_lba, sector_buf) != 0)
  {
    return -5;
  }

  for (uint32_t i = 0; i < sectors_needed; ++i)
  {
    uint8_t temp[512] = {0};

    if (i == sectors_needed - 1 && (num % 512 != 0))
    {
      memcpy(temp, (const uint8_t*)buffer + i * 512, num % 512);
    }
    else
    {
      memcpy(temp, (const uint8_t*)buffer + i * 512, 512);
    }

    if (write_sector(file.data_beginning + i, temp) != 0)
    {
      return -6;
    }
  }

  return sectors_needed * 512;
}